Theodore spencer



2 Sheets-,-Sheet 1.

(No Model.)

T.SPBNGER. TEST AND SIGNAL GIRGUIT AND APPLIANCE.

Inventor.

2 Sheets-Sheet 2.

(No Model.)

SPENCER. TEST AND SIGNAL CIRCUIT AND APPLIANCE.

Patented Oct. 31, 1893.

vw. .n, a RN U .x A sq QR A A A l SET JMQ 4Q 1.... an A. T fi t m M NITED STATES PATENT Enron.

THEODORE SPENCER, OF CAMBRIDGE, ASSIGNOR TO THE AMERICAN BELL TELEPHONE COMPANY, OF BOSTON, MASSACHUSETTS.

TEST AND SIGNAL CIRCUIT AND APPLIANCE.

SPECIFICATION forming part Of Letters Patent No. 507,565, dated October 31, 1893.

Application filed November 19 1892. Serial No. 452, (N m del) To all whom it may concern.-

Be it known that I, THEODORE SPENCER, residing at Cambridge, in the county of Middlesex and State of Massachusetts, have invented certain Improvements in Test and Signal Circuits and Appliances, of which the following is a specification.

This invention relates to telephonic intercommunication. It is frequently desirable to centralize the vitalizing batteries of substation telephone transmitters at the central station, as generally indicated in and claimed by United States Patent No. 252,986, granted to George L. Anders, January 31, 1882; and in doing this to arrange that a battery so centralized, may be common to and capable of being utilized simultaneously bya number of main telephone circuits. Such an arrangement which can readily be made efficient, and under many conditions is very economical, is disclosedin United States Patent No.447,220, granted February 24:, 1891, to Anthony C. White.

In the practical construction and operation of organizations embodying the above mentioned features, it is found convenient and useful to introduce an induction coil between the two portions of the switchboard connecting cord or link connection as substantially disclosed in United States Patent No. 335,436, granted February 2, 1886, to Thomas B. Doolittle, and to relatively dispose the connections and circuits so that in the case of any two circuits connected for intercommunication through the medium of such a compound link connection and interposed induction coil, each of the said two main circuits concerned, shall include a battery or equivalent source of electrical energy, and one of the helices of the induction coil; such an organization in fact as is described in United States Patent No. 474,323, granted May 3, 1892, to Hammond V. Hayes. An arrangement of this kind in which either the same or two distinct batteries may be used, is advantageous, becauseitdividesthe total compound telephone circuit into two distinct conductively complete sections and thereby secures a higher degree of immunity from circuit or battery troubles, and because also it tends to provide a greater uniformity of service, and therefore a better service; for the reasons that each transmitter is required (even though the generator be common to both circuits) to vary the current of its own circuit and generator only; and that its variations can be propagated through the intermediation of the induction coil to the corresponding circuit, where they will be manifested in the receiver. In the practical operation of large telephonic cen- 6o tral stations on these principles, it is obviously desirable that they shall be associated with a multiple switchboard, and it is equally obvious that so associated, asatisfactory and efficient busy test or signal becomes essential. To provide such a satisfactory busy test or a signal, is one of the objects of this invention. When the multipleswitchboard employed is of I the branch terminal type, in which the plug sockets instead of containing separable contacts in series one pair at eachswitchboard i section, comprise normally discontinuous contact springs forming parallel branch connections, one at each section, as described in United States Patent No. 463,54c4, granted 5 November 17, 1891, to Frank A. Pickernell,

it furthermore becomes necessary to so devise or arrange instrumentalities, or means, which during the act of sending an outgoing call signal over any main circuit shall enable the said call to be transmitted without operating a the line or call annunciator 'of such circuit which may be located at some other section of the switchboard, a signal or response from which might beregarded by the operatorthere, 8 5 as anincoming call signal. To prevent the occurrence of such false calls in multiple switchboards operated upon the common centralized battery or generator system, is a second object of this invention.

Though not essential, it is highly advantageous to associate with multiple switchboards embodying the principles outlined above, some simple and efficient means where by the call or line annunciator having given its call signal, may be automatically reset. To provide such a means is the third object of my invention, and I find that it can be attained by the application to the circuit indicating a call, of the same means as I employ in connection with a called circuit for the prevention of false call signals.

To attain these objects, the invention embraces several: features, to wit: a novel and improved busy test apparatus and circuit for a multiple switchboard; the combination with a multiple switchboard adapted for theinterconnection of telephone main circuits whose substation transmitters are provided with current from a centralized and preferably common source of electrical energy, of a busy test apparatus and circuit which depends for its operation upon the connection or nonconnection of the said source with the line tested; a multiple switchboard in which the battery power for the substation transmitters of the several circuits centering in such switchboard may be supplied to any such circuit by the act of making a central office connection therewith, associated or combined with a busy test apparatus and circuit, enabled by a special construction (which may include an electromagnetic or other resistance) to receive for any main circuit its signaling current from the transmitter battery of such main circuit; and the combination in a branch terminal multiple switchboard of a polarized call annunciator or similar signal receiving instrument for each main circuit responsive to currents of given direction; a source of calling current in normally open circuit with each such annunciator; and a suitable circuit closer at each substation adapted when operated to permit an electrical current of suitable direction to pass through and actuate the annunciator, which thus is caused to give the call; with a stronger source of current arranged to be included in the main circuit by the act of making a connection therewith at the central station, either to answer a call, or to send an outgoing call for a desired line, which stronger source is thereupon caused to transmit a currentof opposite direction and greater strength to that of the calling current through the said annunciator, which under the first condition resets the annunciator that has given the call, and which under the second condition prevents the annunciator from responding to outgoing calls.

In the drawings which accompany and constitute a part of this specification, Figure l is a diagram illustrating the several features mentioned above; and Fig. 2 is a diagram of a modified arrangement wherein the transmitter vitalizingbatteries are included in the circuit of the connecting cords, instead of being placed in normally open circuit with one side of the main circuits.

Referring first to Fig. 1, L and L are metallic telephone circuits extending between substations S and S respectively, each to a central station Z where they are represented by springjacks or plugsockets j, one for each line, at the several sections 0, C and C of the switchboard. The calls sent from substation S, are arranged to be answered by the attendant at the switchboard section 0; its call annunciator A, being for that purpose located at such switchboard section; and in like manner as shown the call annunciator A of circuit L is located at section 0 It must however be understood. that in practice the main circuits entering the central station, while represented by plugsockets on each switchboard section so as to be readily accessible for connections desired by other circuits having their calls answered on the said boards, each have their call annunciator-s placed at some one section, the annunciators of the whole being equitably divided between the several sections.

L is an earth completed main telephone circuit, extending between another substation S and the central station, having plugsockets similar to those of circuits L and L Like these also, it has a double conductor through the switchboard, as otherwise it would not be fitted for inter-connection with metallic circuits, and the said conductor is earthed at E Its calls are to be answered at switchboard section 0 and accordingly, its call annunciator A is there placed.

The two conductors of circuit L are respectively marked a, 0, those of L are marked (9 b and those of L, c and c and the spaces or gaps left in the lines representing the several conductors, are intended simply to indicate indefinite lengths of conductor. As shown, the conductors a, b and c are branched to the spring contacts of the springjacks j, and the conductors a b and c are branched to the conducting frame pieces or sockets of the said jacks; which thus are formed into normally incomplete bridges between their circuit conductors. A plug connector 1, formed with two conducting contacts, namely a tip conductor 13, and a stem conductor 9 insulated from one another, will therefore when thrust into any socket make a connection by the said tipp with the spring 31 and by the said stem with the socket frame; and any extension conductors united with the tip and stem (in practice the conductors of a flexible cord) will be connected with the circuit concerned. At the substations, one of the line conductors terminates in the automatic switch lever 5, which when the receiving telephone T is in place on the end thereof, rests on the contact 7, continuing the circuit through the condenser 9, call bell 10 and thence to the return conductor or earth. The condenser as described in Letters Patent No. 474,323 is so proportioned, that the bell 10 can readily be rung through it, by alternating currents, although it affords no passage to steady currents, the circuit thus while the telephone is in place, being open. The telephone being removed from its support, the switchbar retracted by a suitable spring, disconnects the condenser branch, and closes the circuit of the main line through the branch 12 telephone T and transmitter T, and return conductor or earth. At the central station, the switchboard extensions of each circuit are normally discontinuous branches, and in that branch of each to which the spring contacts of the plugsockets are united, but at a point thereof IIS outside of all the said plugsockets is included a main battery B or B which may be commonto a number of main circuits; although as indicated by the drawings, it is preferable that batteries for metallic circuits shall not also be required to serve earth completed circuits. Accordingly, I have shown the battery B as being connected with the two metallic circuits L and L while the earth completed circuit has a difierent battery B The batteries B B as indicated may have their poles connected to omnibus bars 1 and 2,

and 3 and 4, from which connections a, b, c,

y, .2, lead to such circuitsas are to be supplied with current; one battery being as before stated, common to a number of circuits.

There being normally no continuity between the two branch connections of the circuit at the switchboards, it is evident that the batteries B B are normally on open circuit so far as their connection with any given line is concerned; but it is manifest that if by any means the spring and frame of any plugsocket can be united, the substation tele; phone at the same time being displaced, the circuit will be closed and the current of the battery will circulate through the transmitting and receiving telephones T, T

In order that incoming calls may be received at the central station, I provide a polarized or deflecting coil annunciator for each circuit, these being marked A, A A Such an annunciator is looped as at 61 6?, from. the two conductors of each circuitat the points 51 and 52, and in the circuit of such loop isa battery e; which (all circuitsbeingnormallyopen) can of course serve many lines; itis however to be especially observed that this battery is so connected that when the circuit of the transmitter battery B is closed by the insertion of the plug, the two will oppose each other in the annunciator loop 01 d and that since the electromotive force of the battery B is the greater, its current will overpowerthat of e.

The resistance and self induction of the coils of the annunciator A are in a manner well understood, so proportioned that though the loop d d thereof is a permanently closed bridge between the two conductors of the talking circuit, no short-circuiting of the battery B'will supervene; nor will conversation be interfered with.

As indicated by the partially obscured condition of the signal disk in the annunciators A and A of the drawings, the signal is ordinarily not displayed. Ifa current of suitable direction pass through the coils of said annunciators, the signal disk will be displayed as shown at A and this constitutes the call signal. Such a current is developed by the small battery 6 when working alone; and when its circuit is closed and the call sent by the removal of the telephone from its support at the substation. To answer a call, the central station attendant inserts one of the plugs of a pair in a socket of the callingline,

and the two sides of the line circuit are then united through the central station telephones. Having received the instructions of the substation thus answered, and obtained therefrom the number of the line wanted, the second plug of the pair is inserted in a socket of the said second line (provided upon applying the busy test such line be found at liberty) and an outgoing call signal is sent in the usual manner. The second station having been signaled the two lines concerned are united as shown, by means of the plugs P and P and their associated conductors 18 and 19 and 20 and 21; these however in the present instance not being continuously conductive, but connected through an induction coil 2', the conduits 18 and l9 of plug P being connected with one, and the conductors 20 and 21 with the other helix of said coil. By this means, it is evident that the current in each of two circuits so connected will when operated by the current varying transmitter T, actinductively upon the other, and thereby operate the distant receiver. r p

The talking circuit between stations S and S will be readily traced on Fig. 1. Beginning at station Sits circuit proceeds by line a, barl, battery B, bar 2, branch 31, tip p of plug P, wire 19, one coil of inductorium 2,,

wire 18, stem conductor 19 socket s, and re turn conductor a to station S. The circuit of station S is completed vfrom earth E at.

said station by line b, bar 3, battery B bar 4, branch 31 ofline b, ti pp of plug P wire 21, the other coil of inductorium 1', wire, 20, stemp of plugl return conductor 5 through the telephone branch atstation S and finally to earth at E In each of thethree cases considered, in which calling, are closed in different ways through the plug conductors, the presence of the plug in the jack operates to close the circuit of the battery B, first, through the main circuit and substation instruments; and second, through the calling annunciator loop. The drawings illustrate the connections of the lattercircuit in the third case mentioned, and we may readily trace them, beginning at plate 1, battery B, and proceeding by plate 2, switchboard conductor a, jack spring 31, plug tip 10, cord conductor 19, induction coil helix, cord conductor 18, plug stem 19 socket-frame s,-switchboard conductor a point 52, wire 01 battery,

called, or connected circuits IIO 6, annunciator A, wire 61, point 51, and then over conductor a to the starting point. The

batteries Band 6 as before stated, are recircuit connections, the only difference being Thev that telephones, or other appliances arealso included in the call circuit. But in each case, an effect is had upon the polar annunciator A. Being organized to operate and, give the signal with a given direction of current developed by battery e, in the first case the action is that a resultant current of opposite direction passes through its coils, and that the signal having been displayed is automatically replaced or restored. In the second case, the plug being inserted in a socket of the second circuit as an operation preliminary to that of sending the outgoing call, the connection of the vitalizing battery B or B in opposition to the annunciator battery e, causes a resultant current through the annunciator coil, of such a direction as to tend to deflect the armature or needle reversely; and thereby prevents a false call. This is useful when the call is to be sent from a switchboard section, different from that where the said annunciator is located. Vere the battery arranged to coincide in polarity with the battery c, it would be impossible to insert a plug in the socket of any line, without operating the annunciator at its appropriate section. In the third case where the two lines concerned are fully connected, it is obvious that the battery 6 of each is overpowered by the battery 13 and that therefore the annunciators of neither will display the call signal.

The two circuits L and L are shown as being united at the central station for through communication by means of the plugs Pand P and their connecting cords, the looped conductors of the said two cords however having no conductive connection, but being inductively united through the induction coil 2'. Thus, while voice currents have free communication between the two circuits so connectcd, or in other words, while telephonic variations are freely propagated, the battery currents circulating in either have no access to the other, and the circuit of the battery is closed on each line through its own helix of the induction coil and by the insertion of the plug, which thus is a circuit closer. For facility of illustration, none of the regular key board or supervisory apparatus is shown in association with the conductors of these plugs P, P although in practice they are employed, as usual. A second plug and cord connection link is also shown and is assumed to be one of a series located at the switch board section 0 there being of course a similar series at each section to make such connections as are called for. WVith this, I have shown the usual telephone loop key, the supervisory telephones whose connection is controlled thereby, and the disconnecting annunciator, but I have not considered it necessary to show the ringing keys.

P and P are the terminal loop plug connectors each having exactly as in the former set a tip contact 13, and a stem contact surface 19 together with the usual nonconducting handle. The induction coil 1' as in the instance before described, is interposed between the two plugs, the conductors 26 and 27 of plug P forming a loop through one helix, and the conductors 33 and 34 of the other plugP forming aloop through the other helix of said induction coil.

The operators telephones are conventionally represented by the telephone 25, which is in a normally discontinuous bridge controlled by the loop key K between the two plug conductors 26 and 27. The button b of the key is shown as being depressed to connect the telephone, and the circuit of the loop is from the junction point 55 on the tip cor'd conductor 27, to the point 56 on the stem conductor 26, by way of wire 25, contact spring m outer spring n wire 23, telephone coil 70, wire 22, springs nm and wire 24. When the key is undepressed, the said bridge circuit is open between the two sets of contact springs m and n, m and M. In practice a disconnecting annunciator I is looped at the points (1 and r in the stem conductor 26 of the answering plug this being preferably of the same construction as the line drops A; that is to say, being a polarized galvanometer annunciator. From the battery side of each main circuit, at a point 14 external to the connection of the main battery, a testing branch conductor is led, these branches being bunched into a common conductor 13, which is united to one terminal of an auxiliary coil in the several operators telephones, the other terminal of the said auxiliary coil being united at any desired point u, to the tip conductor of the answering plug P which is therefore also a test plug. These appliances constitute the busy test apparatus and circuit; and in the figure, the act of applying such test to the circuit L atthe switchboard section 0 is shown.

when any line is already in use, a connecting plug must certainly be inserted in some one of its plug sockets. In the drawing for example,a plug is seen to be inserted in the socket of circuit L at section 0. The plug inserting operation therefore connects all of the plugsockets of that line with the terminal or pole 4: of battery B by means of a line of conduction to be traced as follows: pole at, conductor b, socket spring 31 of the jack j at C, plug tip p, conductor 21, induction coil t', conductor 20, plugstem socket frame 3 and main conductor b and thereby closes one gap in the test circuit of the battery B which includes the auxiliary telephone coil. The other pole of the said battery B connects with one terminal of the auxiliary telephone coil 70 by way of the poleplate 3, conductor 1), junction point 14:, wires 16 15 and 13. The remaining terminal of the auxiliary telephone coil connects with any eonvenientpoint It on the conductorwhich terminates in the answering plug tip 19. If it be desired that the auxiliary coil connection shall be controlled by the loop key K, as would ordinarilybe the case, the junction point it will be, as shown, at some point between the coil, and the contact 71?. n; but if the connection with said plug tip is for any reason to be permanent, the said junction point may be 10- cated between the said tip 19 and the contact mm. The test circuit being traceable, and the test applied as described above, it is evident that a current from the battery 13 will be directed through the auxiliary coil of the telephone, provided the line be busy,producing a distinct click in the said telephone, which is held to the ear of the testing operator, the circuit of said current being from one pole of the battery to the other, by Way of pole plate 4, conductor b, jackspring 31, tip 1), conductor 21, induction coil helix 2', conductor 20, stem conductor 19 socket frame 8, conductor 19 socket frame 8 at section 0 tip 10 of plug P conductor 27, junction point 55, w1re 24, contact spring m, outer contact'spring n, w1re 22, auxiliary coil k of telephone t, wire 13, wires 15 and 16, point 14, conductor 19 of the main circuit L and pole plate 3. If on the contrary, the tested circuit be at liberty, no sound will be heard in the telephone at the moment of applying the plug tip to the socket frame, because the test circuit will not have theretofore been made continuous between the spring and frame of any. other socket of the same line, and consequently,

the potential of the remaining socket frames 8f the same line will be at its normal condi- In some cases, such for example where the telephone circuits supplied by the battery B are of considerable length and require a strong battery it is desirable to subdue the effect produced by the derived current upon the telephone and to moderate the loudness of the audible signal due thereto. This is done by introducing a suitable resistance or retardation coil f into the test circuit as shown; if a simple resistance coil be employed, it should be of much higher real resistance, than is required for a retardation coil or electro magnetic resistance. I have found a retardation coil having a real resistance of four hundred ohms, and an apparent resistance to telephone currents of ten thousand ohms to answer well; and this may be placed as shown in the individual test branch of each main circuit in the common conductor leading to the several operators telephones; or in the circuit of the auxiliary coil of each telephone at pleasure.

In the modification indicated by Fig. 2, two metallic circuits L and L are shown. The direct circuit of a single pair of connection plugs P P also is shown, as is also the bridge connection of the operators telephones and the auxiliary test coil thereof. Instead however of connecting the vitalizing batteries for the transmittersin the normally discontinuous spring-jack conductor of the several main circuits, theyare introduced into the circuit of the conductor connecting the plugs with the interposed induction coil. There is however no change in the circuits in virtue of this change in the position of the battery;theelectricalconnectionsbeingidentical. It is sometimes advantageous to interposethe disconnecting annunciator I as shown in Fig. 2 in the circuit of the conductor 34 leading from the tip of the answering plug to the loop key, instead of placing it in' the stem conductor thereof. In that case it can, if desired, serve also as a visual busy test signal, it being in that portion of the circuit of the plug tip which is common to the main circuit and the busy test derived circuit.

Having now fully described. the invention and its mode of operation, I claim 1. The combination in a multiple switch board of a series of main telephone circuits each having two switchboard conductors; a

series of springjacks for, each circuit, each having a spring contact terminal, and a socket contact terminal normally in a sepaterposed induction coil, and a loop circuit" from the two plugs to the two induction coil helices respectively; the said plugs being adapted to' be inserted in the said springjacks, and thereby to inductively unite any two main circuits, to close each of the circuits through the said battery and one of the induction coil helices, and to connect the socket terminal of each spring jack with the spring terminal thereof, and with one pole of the battery through the said helix; with a busy test apparatus comprising the socketcontact terminals of the said springjacks of the main circuits; an electro magnetic signaling instrument; a branch circuit extending from the other pole of the said main circuit transmitter battery to one terminal of said signaling instrument; and a test plug with a conducting tip, adapted to be applied to the said socket terminals, and having a flexible conductor uniting the said tip to the remaining terminal of said signaling instrument, substantially as described.

2. In a multiple switchboard a busy test circuit and apparatus comprising a series of double conductorspring-jacks or plug sockets for each main circuit, each containing a spring contact branched from one main circuit conductor, and a frame contact branched from the other main line conductor of thesame circuit; a main circuit transmitter battery or other generator having one pole connected with the said spring contacts: means for uniting the said two contacts electrically by the act of making a main circuit connectionand for thereby connecting the said battery pole with the several other socket frame pieces of said main circuit; a test circuit conductor extending from the remaining pole ofsaid trans mitter battery to a contact piece mounted on. the tip of a test plug; and an electro-magnetic signaling instrument included in the circuit of said test conductor, and adapted to become operative and give the busy signal when the test circuit is closed by the application of the tip of the test plug to the frame of a springjack of a line in use, substantially as described.

3. In a multiple switchboard, a busy test circuit and apparatus, comprising a series of double conductor spring jacks or plug sockets for each main circuit, each containing a spring contact branched from one main circuit conductor, and a frame contact branched from the other main circuit conductor, the said two contacts being normally separated; a main circuit transmitter battery having one pole connected with the series of spring contacts; a main circuit connection plug adapted to fit said sockets to unite said spring and frame contacts, and thereby to unite said battery to all other frame contacts of said main circuit; a test "circuit conductor extending from the remaining pole of said transmitter battery to a contact piece mounted on the tip of a testing plug which tip contact piece to make this test is adapted to be brought into contact with the jackframe of a line to be tested; and a telephone included in the test circuit so formed, and organized to produce an audible signal when a line already in use is tested, substantially as described.

4. The combination of a series of spring jacks or plug sockets interposed in a multiple switchboard in parallel branches between the two conductors of a main telephone circuit, and each comprising a socket or frame contact piece and a spring contact piece normally separated or insulated from each other, the several spring contacts being branched from one and the several socket contacts being branched from the other of said main circuit conductors; a transmitter battery for the said main circuit having one of its poles connected with said spring contacts; a loop plug,and a closed loop connected therewith, adapted to fit the said springjack and to electrically unite the two contacts thereof, and thereby to change the potential of the frame contacts of the remaining jacks of the same series: a test circuit conductor branched from the other pole of said transmitter battery to the conducting tip of a test plug whereby the test circuit may be closed by applying the said conducting tip to the frame piece of a jack of a busy circuit; and a telephone having an inducing coil included in circuit with said branch conductor, and thereby organized to produce an audible signal when the said test is closed substantially as described.

5. The combination with a multiple switchboard, a series of main telephone circuits connected therewith each provided with a number of normally open plug sockets or springjacks interposed between its two conductors or sides, and a centralized source of current which may be common to a number of said main circuits, and which has one pole in normal connection with the spring contacts, but disconnected from the conducting frame pieces of said springjack; of a busy test apparatus consisting of a test plughaving aconducting piece to be placed in contact with the frame piece of a springjack whose line is to be tested; means as indicated for altering the potential of the frame pieces of a busy line, or for connecting such frame pieces with the said source of current when a connection is made with any springjack of the same series; an electromagnetic testing instrument such as a telephone; and a test circuit branch conductor extending from the other pole of said source of current, through the said instrument to the conducting piece of said test plug, substantially as and for the purposes described.

The combination of a number of series of multiple switchboard springjack connections, each springjack having a spring contact piece and a socket or frame contact piece in a separated relation, the said separated contact pieces of the springjacks of each series constituting respectively the disunited terminals of a main telephone circuit, and also of a busy test circuit; a main circuit transmitter battery or generator included in and forming a portion of both of the said norm ally open circuits; a circuit closing plug adapted to fit said springjacks to unite the separated contacts thereof, and thereby to close the main line circuit through said generator, and to connect with said generator the socket contact pieces of the remaining springjacks of the sameseries, whereby each is made a terminal of the test circuit; an electro magnetic signal instrument included in the said test circuit; and a test plug forming the complementary terminal of said test circuit which may be finally closed by the application of said plug to any of the said re maining frame contact pieces; substantially as described.

7. The combination in a multiple switchboard, of a number of substation telephone circuits; a series of springjacks for each circuit, each springjack having a spring terminal and a socket terminal,normally in aseparated relation; a normally open centralized transmitter battery supplying current for said circuits,and connection cords fitted with terminal plugs adapted to be inserted in said springjacks, and thereupon to unite the circuits concerned, and also to electrically connect the two springjack terminals, thereby closing the circuit of the main circuits through the battery, and connecting the socket terminals of the other springjacks of the same circuit with one pole of said battery; with a test plug having a conducting tip; a branch conductor for each main circuit uniting the remaining pole of said battery with said conducting tip; and an electro magnetic testing instrument such as a telephone interposed in the circuit of said branch conductor substantially as described.

8. The combination, substantially as hereinbefore described, in a multiple switchboard, of a number of substation telephone circuits; a series of springjacks for each circuit, each springjack having a spring terminal and a socket terminal normally in a separated relation; a normally open or disconnected centralized transmitter battery supplying current for said circuits; and terminal loop plugs fitted with flexible conductor attachments adapted to be inserted in said springjacks and thereupon to unite the circuits concerned, and to electrically connect the two springjack terminals, thereby closing the circuit of the main circuits through the battery, and connecting the socket terminals of the other springjacks of the same circuit with one pole of said battery; with a test plug having a conducting tip, a branch conductor for each main circuit, uniting the remaining pole of said battery with the tip of said test plug; an electromagnetic or other resistance, and a signal receiving instrument such as a telephone interposed in thecircuit of said branch conductor; substantially as described.

9. In a branch terminal multiple switchboard, the combination of a main telephone circuit extending between a central station and a substation; a polarized call annunciator in such circuit at the central station, responsive to currents of uniform direction; a source of calling current in normally open circuit with said annunciator; and a suitable circuit closer at the substation, adapted to close the circuit of said source through said annunciator in such direction as to give the signal; with a stronger source of current adapted to be included in the main circuit by the act of making a connection at the central station with said circuit, and thereupon to direct through said annunciator a current of greater strength, and opposite direction, whereby the said annunciator if operated, may be reset, and otherwise may be prevented from operating, substantially as described.

10. The combination substantially as here- 'inbefore described, of an open main circuit;

a polarized signal instrument included therein; a circuit closer therefor; a battery also included therein, and arranged on the operation of said circuit closer to direct a current of electricity through said instrument of proper direction to actuate the same; with a normally discontinuous loop of said circuit, shunting the said battery and the polarized signaling instrument, a circuit closer therefor; and a second battery of higher electro-motive force included in said loop, the said second battery being so arranged that upon the closure of said loop by the operation of its circuit closer, it will oppose the smaller battery and cause a resultant current of opposite direction to flow through the helices of the polarized signal instrument, thereby acting to prevent the operation of the signal, or to reset the same, if already given. H

11. The combination of a series of main said conductors; a normally incomplete busy test circuit for each main circuit at each switchboard section, including a conductor extending from a point on the said direct main circuit conductor external to the outermost springjack branch,and branching to test plugs at the several sections through the operators telephone at such section, the several springjack branches of the series being common to both main and test circuits; a mainline transmitter batteryincluded in the said direct main circuit conductor between the junction point of the busy test branch and the outermost springjack, and being thereby made common to the said main and test circuits, but having its circuits normally incomplete in said springjacks; and circuit closing plug connectors at each switchboard section adapted to be inserted in the said springjacks, and thereby to complete the bridge connection thereof, to close the main line circuit through the said battery, and to connect with said battery the return conductor side of the remaining springjacks of the series; substanw tially as described and for the purposes set forth. I

12. A series of springjacks on a multiple switchboard whose frame contact pieces and spring contact pieces are normally in a sepa rated relation; conductors representing respectively the direct and return conductors of a main telephone circuit, one branching to all of the spring contacts, and the other to all of the frame contacts of a series of springjacks; a main circuit transmitter battery interposed in the spring branching conductor ata point outside of the outermost springjack; a circuit closing plug for said springjacks adapted to be inserted therein and to electrically unite the separated contacts thereof, for the purpose of closing the main circuit through the battery, and of connecting one pole of said battery to all other frame contact pieces of the same series of springjacks; and means for' testing for the presence of the said battery connection at any of the several springjack frames consisting of a conductor branched from the other pole of said battery to one terminal of the operators telephone, and a movable conductor and testing plug for placing the other terminal of said telephone in contact with any of the said springjack frames, substantially as described.

In testimony whereof I have signed my name to this specification, in the presence of two subscribing witnesses, this 11th day of November, 1892.

. THEODORE SPENCER.

Witnesses:

GEo. WILLIs PIERCE, FRANK O. LOOKWOOD. 

